The manufacture of integrated circuits involves the transfer of geometric shapes on a mask to the surface of a semiconductor wafer. Thereafter, the semiconductor wafer corresponding to the geometric shapes, or corresponding to the areas between the geometric shapes, is etched away. The transfer of the shapes from the mask to the semiconductor wafer typically involves a lithographic process. This includes applying a solution of a pre-polymer solution to the semiconductor wafer, the pre-polymer being selected to form a radiation-sensitive polymer which reacts when exposed to ultraviolet light, electron beams, x-rays, or ion beams, for example. The solvent in the pre-polymer solution is removed by evaporation, and the resulting polymer film is then baked.
The film can be exposed to radiation, for example, ultraviolet light, through a photomask supporting the desired geometric patterns. Soaking the wafer in a developing solution then develops the images in the photosensitive material. The exposed or unexposed areas are removed in the developing process, depending on the nature of the radiation-sensitive material. Thereafter, the wafer is placed in an etching environment, which etches away the areas not protected by the radiation-sensitive material. Due to their resistance to the etching process, the radiation sensitive-materials are also known as photoresists, and the term photoresist is used hereinafter to denote such radiation-sensitive polymers and their pre-polymers.
Thus, when patterning is performed by etching, a resist film mask having a desired pattern is generally formed on a layer to be etched, and the layer is etched by the use of the mask. A resist film for forming a mask is normally formed on a layer to be etched by coating a resist on a wafer using a resist coater and baking the resist. A prior art resist coater for coating a resist on a wafer is explained with reference to FIG. 1. FIG. 1 is a sectional view showing a structure of a prior resist coater of a spin coat type.
As shown in FIG. 1, a resist coater 10 has a wafer holding table 12 for rotating a wafer W around an axis, which can be perpendicular to the wafer W while holding the wafer W with a wafer surface thereof directed upwardly. A resist supply nozzle 14 supplies resist to the wafer W, which may be held on the wafer holding table 12. A coater cup 16 generally surrounds the wafer holding table 12 and the resist-supplying nozzle 14.
The wafer holding table 12 is generally attached on an upper end of a rotation shaft 18 which penetrates a bottom portion of the coater cup 16 and which may be rotated with a rotation device (not shown). The wafer holding table 12 is generally provided on its wafer holding surface with a chuck mechanism for vacuum-sucking the wafer W, and it can be rotated together with the rotation shaft 18 around an axis, which is generally perpendicular to the wafer holding surface.
The coater cup 16 can trap resist particles, which are generally scattered from the wafer W by a centrifugal force due to the rotation of the wafer W. The coater cup 16 generally possesses an outer cup 20 for trapping resist particles which may be scattered in sidewise and upward directions, and an inner cup 22 for guiding resist particles, which can be scattered in a downward direction from the wafer W to a bottom portion of the outer cup 20.
The outer cup 20 has at an upper portion thereof an opening 24 for introducing the resist supply nozzle 14 or the like, and for taking in and taking out the wafer W. Furthermore, the inner cup 22 is generally provided on a lower portion of the outer cup 20, and the inner cup 22 has a cylindrical portion 22a, and an umbrella portion 22b which spreads toward the inside of the coater cup 16 from an upper opening thereof.
The resist supply nozzle 14 can be lowered via the opening 24 of the coater cup 16, and is generally arranged at a position facing a resist coating surface of the wafer W. Also, in order to clean an edge to the back surface of the wafer W, a first cleaning nozzle 26 for spraying rinse agent can be directed toward the edge of the back surface of the wafer W through the bottom portion of the coater cup 16. Furthermore, in order to clean an edge of the surface of the wafer W, a second cleaning nozzle 28 for spraying rinse agent may be directed toward the edge of the wafer W via the upper opening 24 of the coater cup 16. Exhaust pipes 30 are generally connected to an exhaust device (not shown) for exhausting the inside of the coater cup 16, and a drain pipe 32 for exhausting the resist trapped in the coater cup 16 are connected to the bottom portion of the coater cup 16.
FIG. 1 is thus presented for illustrative and background purposes only. In typical prior art coater cup designs a mist generation mechanism may be relied upon. The wafer generally rotates when the photoresist and solvent are dispensed onto the wafer. The photoresist can thus be coat the wafer through wafer spinning techniques. An edge photoresist can be removed through solvent dispensation. Typically, photoresist dust can result from such a semiconductor fabrication operation and normally should be exhausted by a proper airflow. More often than not, however, the dust is splashed back, thereby forming contaminants and other particles, which result in semiconductor defects. When such contaminant or dust piles up, exhaust lines can choke up. Thus, not enough exhaust may result. The semiconductor fabrication devices in question cannot determine whether such “splash back” is the root cause of decreases in exhaust. Such splash back generally results in manufacturing problems and poor semiconductor device yields.
The present inventor has thus concluded, based on the foregoing that a need exists for an improved method and system for checking contaminants, such as dust, during spin coating and other similar semiconductor fabrication operations. If such contaminants can be detected utilizing a non-evasive detection technique, the semiconductor fabrication operation can be automatically halted to prevent further scattering of contaminants, such as photoresist (PR) dust. The present invention thus meets and solves this important need.